The majority of CO alarms tend to fall into one of two groups. The first group of alarms are basic alarms that, when activated, provide a visual alarm warning display via a number of light emitting diodes (LEDs) and an audible warning via a horn. The second group of alarms are more expensive devices which have an LCD display which allows specific messages to be displayed.
A disadvantage with the cheaper LED only alarms is that, in the event of a product malfunction, being able to identify quickly the nature of the issue is difficult. A display of specific error codes can only be achieved by a combination of lit or flashing LEDs, which can be difficult to interpret. The more expensive LCD alarms can display specific error codes on the LCD. However, even here, only a very small amount of information can be displayed at the same time.